The disclosed combustion pressure control device, which is of an internal combustion engine having precombustion chambers (61a-61d) that respectively interconnect with combustion chambers (5a-5d), is provided with a spring device that has elasticity and of which one end is connected to the precombustion chamber that interconnects with one combustion chamber, and of which the other end is connected to the precombustion chamber that interconnects with another combustion chamber. The spring device contains a fluid-encapsulating member (63). When the pressure of at least one of the one combustion chamber and the other combustion chamber reaches a control pressure within the period from the compression stroke to the expansion stroke of the combustion cycle, the volume of the precombustion chamber increases and the pressure increase of the combustion chamber is suppressed by means of the spring device contracting.